Host defense responses restricts the growth of the fungus Colletotrichum lindemuthianum in cowpea, TE 97 411-1E resistant genotype.

Cowpea is the main subsistence crop in the semiarid North-east of Brazil. However, very few is known concerning to its defense mechanisms against fungi. The objective of this present work was to evaluate the infection strategies of the hemibiotrophic fungi Colletotrichum lindemuthianum and the associated cytological defense responses of two cowpea genotypes, TE 97-411-1E (resistant) and BR 3 Tracuateua (susceptible). The infection process of the fungi in both genotypes occurred preferentially through the leaf epidermal cells by penetration tubes emerged from appressoria. The resistant cowpea genotype, TE 97-411-1E, showed enhanced penetration resistance to C. lindemuthianum associated with higher epidermal H2O2 accumulation, papilla formation, and increase in phenylalanine ammonialyase activity, possibly related to accumulation of phenolic compounds and host cell wall lignification. Macroscopic examination of the primary leaves revealed the presence of shrunken necrotic lesions characteristic of anthracnose in infected BR 3 Tracuateua, whereas in TE 97-411-1E cell death was also observed but only in a reduced percentage of the infection sites. In summary the results obtained in the present study suggested that TE 97-411-1E genotype is more resistant to C. lindemuthianum compared to BR 3 Tracuateua, as it developed more effective defense responses against the establishment of the pathogen